| Joan of Penthièvre | |
|---|---|
.jpg) Tomb of Jeanne de Penthièvre, Duchess of Brittany | |
| Duchess of Brittany | |
| Reign | 30 April 1341 –1365 (disputed suo jure) 1365–10 September 1384 (titular) |
| Predecessor | John III |
| Successor | John IV |
| Born | 1319 |
| Died | 10 September 1384 (aged 65) Guingamp |
| Burial | church of the Friars Minor of Guingamp. |
| Spouse | Charles I, Duke of Brittany |
| Issue | John I, Count of Penthièvre Guy Henry Marie, Lady of Guise Marguerite, Countess of Angoulême |
| House | Dreux |
| Father | Guy de Penthièvre |
| Mother | Jeanne d'Avaugour |
| Religion | Roman Catholicism |
Joan of Penthièvre (French: Jeanne de Penthièvre; c. 1319 – 10 September 1384) reigned as Duchess of Brittany together with her husband, Charles of Blois, between 1341 and 1364. Her ducal claims were contested by the House of Montfort, which prevailed only after an extensive civil war, the War of the Breton Succession. After the war, Joan remained titular Duchess of Brittany to her death. She was Countess of Penthièvre in her own right throughout her life.